This application generally relates to vehicle transmissions. More particularly, this invention relates to a transmission system that predicts and identifies coast starts, and which directly or indirectly controls clutch operation under coast conditions.
A variety of vehicle transmissions are available currently in the market. Some transmissions are automated and do not require operator input other than selecting a gear mode, for example, reverse or drive. Other transmissions are manual and require manual operation of a gear shift lever to manually move transmission components into selected gear ratios. Manual transmissions typically require manual actuation of a clutch pedal to eliminate the connection between an engine output shaft and an input shaft of the transmission. Manual clutch pedal actuation is typically required each time that a shift in gears is desired.
More recently, suppliers and vehicle manufactures have been attempting to simplify the operation of manual transmissions. Even with such improvements, those skilled in the art are always striving to make transmission systems operate more efficiently and to provide a smoother, more comfortable ride. One problem that has not been addressed relates to vehicles experiencing a coast start. This typically occurs when a vehicle, such as a heavy duty truck, is stopped on an incline and the vehicle gains speed without requiring a vehicle operator to depress a vehicle throttle pedal. In order for clutch to be moved into an engaged position, the engine output shaft and transmission input shaft speeds should be very close to each other. Typically, during a coasting condition, once the input shaft speed has exceeded a predetermined speed threshold, the engine revolutions per minute (RPM) are increased so that the clutch can be engaged. The system typically does not take into consideration other vehicle operating factors such as vehicle speed, engine speed, etc., before taking action to engage the clutch. Thus, the engine speed may be increased and the clutch engaged during unfavorable conditions. This is undesirable because due to the sudden closure or engagement of the clutch, there is a surge in the drivetrain. This can cause overloading or shock loading of certain drivetrain components, resulting in premature wear or failure.
Another problem with coast starting concerns gear ratios. The transmission system does not adjust the transmission gear ratio in response to a coast start. This can result in a harsh or abrupt transition as the clutch is moved into the engaged position, causing discomfort to vehicle occupants.
While it is desirable to have a closed driveline, i.e. an engaged driveline, at all times at speed unless a shifting operation is taking place, there are certain operating conditions in which it is desirable to have an open driveline, i.e. a non-engaged driveline. The subject invention provides a control system and method that determines when a vehicle is experiencing a coast start, and which engages or disengages a transmission component as needed to achieve smooth and efficient vehicle transmission operation.